Seems like facebook has some kind of DNS-Problem right now(#facebookdown). To fix this enter the facebook IPs in your hosts-file. To get them, have a look at your DNS Cache with a tool like dig(or use the ones I provide below).

Windows
Windows has a similar file, which is located in %SystemRoot%\system32\drivers\etc\hosts. Where %SystemRoot% is your Windows directory, so most likely C:\Windows.

At least in Windows 7 the file is locked by the system, so unless you have notepad++, which doesn’t care about all this, you have to open your explorer, go to C:\Windows\system32\, right-click notepad.exe and select „start with admin rights“(or something like that…). Then click File/open, go to C:\Windows\system32\drivers\etc and select „all files“ on the right side(see screenshot). Then again open the file and enter the following:

66.220.158.16 facebook.com
66.220.158.16 www.facebook.com

MacOS

1. Click on the looking glass icon in the top right corner of the screen
2. Type „Terminal“ and press Enter, a new app called „Terminal“ will appear
3. Don’t get confused by it, just follow the steps
4. Copy this text into your clipboard : echo „173.252.101.16 www.facebook.com“ | sudo tee -a /etc/hosts
5. Paste it into the „Terminal“ window and press Enter
6. You will be prompted to enter your password (it will not show up on the screen, don’t worry about it), press Enter again when you finished typing your password.
7. The line „173.252.101.16 www.facebook.com“ will appear on the screen.
8. Done!